Overheard: Apple Wipes Shine Off GT Advanced

Updated Sept. 11, 2014 11:03 pm ET

Apple's apparent decision to not put sapphire screens on its new iPhones has broken the market value of GT Advanced Technologies. From Apple's introduction of its new iPhone's Tuesday through Wednesday's close, GT Advanced shares plunged more than 25%.

But investors should have seen the cracks coming. GT Advanced is building a sapphire-manufacturing facility in Arizona in partnership with Apple, which already uses the highly durable material in parts of its iPhone 5S. Many investors had speculated sapphire would replace Gorilla...